The present invention relates generally to the measuring art, and more specifically to a new and useful system for measuring coating thicknesses utilizing beta backscatter radiation techniques.
The beta backscatter radiation technique for measuring ultra thin coating thicknesses is well known, being disclosed in U.S. Pat. No. 3,132,248 among others, and various types of apparatus have been developed for use in conjunction therewith. U.S. Pat. No. 3,115,577, for example discloses a measuring table having interchangeable apertured platens for supporting a workpiece to be measured in operative alinement with a radiation source and detector, together with an illuminating arrangement to facilitate positioning of the workpiece. U.S. Pat. No. 3,705,305 shows another table arrangement for supporting a workpiece to be measured, the table carrying a measuring head including a source and a detector, and a sighting device to align the workpiece for measurement. The measuring head is rotatable on the table for supporting the workpiece on the head itself.
For many purposes it is undesireable, if not impractical or impossible to bring the workpiece to be measured to such a table, and portable probes have been developed which can be positioned either directly on the workpiece under test or on a surface on which such workpiece is placed. U.S. Pat. No. 3,720,833, for example, shows a housing adapted to be placed, for example, directly on a circuit board, the housing containing a locator and a probe including both a radiation source and a radiation detector. When the locator has been used to position the coating under test relative to the housing, it is retracted and the probe is simultaneously lowered into position against the coating area under test, to make the measurement.
Another portable probe is shown in U.S. Pat. No. 3,529,158 wherein a guide receptacle is adapted to be positioned relative to the coating area under test, the guide then being removed from the receptacle, and replaced by a portable probe which also can be installed on a table to receive and support a coated object under test.